Multiphase Ceramic Material With Giant Dielectric Constant, And Preparation Method Thereof

Abstract

The present invention discloses a multiphase ceramic material with a giant dielectric constant, wherein the multiphase ceramic material has a general formula of A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2; wherein A is at least one selected from the group consisting of Nb, Ta, V, Mo, and Sb, B is at least one selected from the group consisting of In, Ga, Al, Co, Cr, Sc, Fe (III), and a trivalent rare-earth cation; n is a molar ratio of B to A, 1<n.ltoreq.5 , 0<x.ltoreq.0.1. The multiphase ceramic material possesses outstanding properties including a giant dielectric constant, a low dielectric loss, and excellent frequency- and temperature-stability. In particular, it exhibits a high insulation resistivity of higher than 10.sup.11 .OMEGA.cm and a high breakdown voltage, which implies it can be applied in high-energy storage devices and supercapacitors. This invention also provides a method to synthesize the multiphase ceramic material.

Description

FIELD OF THE INVENTION

[0001] This invention relates to a multiphase ceramic material with a giant dielectric constant and its preparation method.

BACKGROUND OF THE INVENTION

[0002] Researches on the miniaturization of high-energy storage devices, supercapacitors and other equipment have shown that as an indispensable part of these devices and equipment, the dielectric material needs to simultaneously possess a giant dielectric constant, a low dielectric loss, and good frequency- and temperature-stability, and the high breakdown strength. The capacity of the energy storage device/equipment is proportional to the square of the working voltage of the dielectric material, suggesting that it is necessary to study the breakdown strength of dielectric ceramic materials.

[0003] Numerous studies have shown that ferroelectric materials, such as BaTiO.sub.3, have a high dielectric constant. However, their dielectric constant is highly dependent on temperature. For other non-ferroelectric materials, such as CaCuTi.sub.3O.sub.12 (CCTO), doped NiO and La.sub.2xSr.sub.xNiO.sub.4 (x=1/3, 1/8), etc., although their dielectric constant can reach 10.sup.5 or more within a wide temperature range, their dielectric loss is very high (>0.1).

[0004] Therefore, there is a need to prepare a dielectric ceramic material with a high dielectric constant, a low dielectric loss, good temperature- and frequency-stability, and high breakdown strength.

SUMMARY OF THE INVENTION

[0005] The objective of the present invention is to provide a multiphase ceramic material with a giant dielectric constant to overcome the deficiencies of the prior art.

[0006] The technical solution of the present invention is a multiphase ceramic material with a giant dielectric constant, wherein the multiphase ceramic material has a general formula of A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2, wherein A is at least one selected from the group consisting of Nb, Ta, V, Mo, and Sb, B is at least one selected from the group consisting of In, Ga, Al, Co, Cr, Sc, Fe (III), and a trivalent rare-earth cation; n is a molar ratio of B to A, 1<n.ltoreq.5, 0<x.ltoreq.0.1.

[0007] The multiphase ceramic material of the present application possesses outstanding dielectric properties including a giant dielectric constant, a low dielectric loss, and good frequency- and temperature-stability. In particular, it exhibits a high insulation resistivity and a high breakdown voltage. The ceramic material has an insulation resistivity of higher than 10.sup.11 .PSI.cm; it can be applied in high-energy storage devices and supercapacitors.

[0008] Preferably, a primary phase of the ceramic material is A.sup.5+ and B.sup.3+ co-doped rutile TiO.sub.2, a secondary phase of the ceramic material is B.sub.2TiO.sub.5; the secondary phase is evenly dispersed in the primary phase. The primary phase provides the multiphase ceramic material with the giant dielectric property, while the secondary phase exhibits excellent electrical insulation properties. The secondary phase is discontinuously and uniformly distributed around the grain boundary of the primary phase. Therefore, it can effectively block the transfer of weakly bounded charges, which contributes to increasing the working voltage and breakdown voltage of the material. Meanwhile, the existence of the secondary phase does not cause the deterioration of the giant dielectric property of the material.

[0009] More preferably, the secondary phase is B.sub.2TiO.sub.5 with an orthogonal structure. During a one-step synthesis process, the secondary phase has a lower synthesis temperature comparing to that of the primary phase, helping to separate two phases.

[0010] Preferably, the multiphase ceramic material has a resistivity of higher than 10.sup.11 .OMEGA.cm.

[0011] Preferably, the multiphase ceramic material has a dielectric constant of higher than 10,000 at a frequency of 20 Hz to 2.times.10.sup.6 Hz; the multiphase ceramic material has a dielectric loss of less than 0.05 before 2.times.10.sup.5 Hz.

[0012] Preferably, the multiphase ceramic material has a dielectric constant of higher than 10,000 from -160.degree. C. to 170.degree. C.; the multiphase ceramic material has a dielectric loss of less than 0.05 from -50.degree. C. to 150.degree. C.

[0013] The present invention also provides a method of preparing the multiphase ceramic material with a giant dielectric constant, the method comprises steps of:

[0014] (1) weighing reactants, which comprise a titanium source, an A source, and a B source, according to a general formula of the multiphase ceramic material, A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2;

[0015] (2) ball-milling in a ball-milling tank and drying to obtain a homogeneous mixture powder;

[0016] (3) transferring the mixture powder into a mortar; pure water is added, and the weight of the pure water is 5%-10% of the weight of the mixture powder; mixing thoroughly; transferring the mixture powder into a die, pressing at a pressure of at least 400 MPa to obtain a green pellet; placing the green pellet in a mortar; pulverizing and grinding the green pellet to obtain a preliminary powder;

[0017] (4) transferring the preliminary powder into a die; pressing at a pressure of at least 2 MPa, followed by sintering; sintering parameters comprise heating rate: 1.5.degree. C./min-15.degree. C./min, temperature: 1200.degree. C.-1500.degree. C., holding time: 1 h -24 h; after sintering, the product obtained is naturally cooled down to room temperature to obtain a dense ceramic pellet;

[0018] (5) polishing a surface of the dense ceramic sheet, followed by annealing; annealing parameters comprise heating rate: 1.5.degree. C./min-15.degree. C./min, temperature: 1000.degree. C.-1200.degree. C., holding time: 1 h-24 h; after annealing, the product obtained is naturally cooled down to room temperature to obtain the multiphase ceramic material with a giant dielectric constant.

[0019] Preferably, in step 1, the titanium source is TiO.sub.2, the A source is A.sub.2O.sub.5, the B source is at least one selected from the group consisting of B.sub.2O.sub.3, B.sub.2(C.sub.2O.sub.4).sub.3, B.sub.2(C.sub.2O.sub.4).sub.3 hydrate, B(NO.sub.3).sub.3, B(NO.sub.3).sub.3 hydrate, B.sub.2(SO.sub.4).sub.3, B.sub.2(SO.sub.4).sub.3 hydrate, B.sub.2(CO.sub.3).sub.3, B.sub.2(CO.sub.3).sub.3 hydrate, B(C.sub.2H.sub.3O.sub.2).sub.3, B(C.sub.2H.sub.3O.sub.2).sub.3 hydrate.

[0020] The non-oxide B source can reduce the synthesis temperature of the secondary phase and reduce its mobility around the grain boundary, helping to form a discontinuously and uniformly distributed B phase.

[0021] Preferably, the ball-milling in step (2) comprises using ethanol or acetone as a dispersant, and using yttrium-stabilized zirconia balls as a ball-milling medium; ball-milling is performed for more than 12 hours; in steps (4) and (5), an atmosphere for the sintering and the annealing is air.

[0022] Preferably, the polishing of the surface in step (5) comprises rough polishing the surface by a 240-grit sandpaper, followed by finely polishing the surface by a 1200-grit sandpaper

[0023] Compared with the prior art, the advantages of the present invention are discussed below.

[0024] In the present invention, rutile titanium dioxide is chemically modified by co-doping A.sup.5+ and B.sup.3+ metal ions to obtain a multiphase material, in which the primary phase is A.sup.5+ and B.sup.3+ co-doped rutile TiO.sub.2 and the secondary phase (B.sub.2TiO.sub.5) is evenly dispersed in the primary phase. The multiphase ceramic material of the present application has outstanding properties including a giant dielectric constant, a low dielectric loss, and good frequency- and temperature-stability. In particular, it has a high insulation resistivity and a high breakdown voltage. The ceramic material can be used in high-energy storage devices and supercapacitors. Its detailed advantages are:

[0025] (1) The primary phase of the multiphase ceramic material with a giant dielectric constant is A.sup.5+and B.sup.3+co-doped rutile TiO.sub.2, and the secondary phase of the ceramic material is B.sub.2TiO.sub.5. The secondary phase is evenly dispersed in the primary phase.

[0026] (2) The multiphase ceramic material has a high insulation resistivity and a high breakdown voltage. The ceramic material has an insulation resistivity of higher than 10.sup.11 .OMEGA.cm.

[0027] (3) At the frequency range of 20 Hz to 2.times.10.sup.6 Hz and at the temperature range of -160.degree. C. to 170.degree. C., the dielectric constant (>10.sup.4) of the multiphase ceramic material shows very little frequency- and temperature-dependency. The dielectric loss of the ceramic material is less than 0.05 before 2.times.10.sup.5 Hz from -50.degree. C. to 150.degree. C.

BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 shows the XRD spectra of the multiphase ceramic material of embodiment 1 and embodiment 2.

[0029] FIG. 2 shows the backscattered electron (BSE) images and the secondary electron (SE) images of the multiphase ceramic material of embodiment 1 and embodiment 2.

[0030] FIG. 3 illustrates the frequency-dependent dielectric properties of the multiphase ceramic material of embodiment 1, which is measured at room temperature.

[0031] FIG. 4 illustrates the temperature-dependent dielectric properties of the multiphase ceramic material of embodiment 1 with four selected frequencies (100 Hz, 1 kHz, 10 kHz and 100 kHz) embodiment.

[0032] FIG. 5 is a backscattered electron (BSE) image of the multiphase ceramic material of embodiment 2.

DETAILED DESCRIPTION OF EMBODIMENTS

[0033] The objectives, technical solutions, and beneficial effects of the present invention will be described below with reference to the accompanying drawings and embodiments.

Embodiment 1

[0034] Embodiment 1 is one of the embodiments in the present invention. The multiphase ceramic material of this embodiment has a general formula of A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2, where A is Nb, B is In, x=0.0125, and n=2.

[0035] The detailed method to synthesize this embodiment comprised the following steps:

[0036] (1) 0.2492 g Nb.sub.2O.sub.5, 0.5206 g In.sub.2O.sub.3, and 11.5312 g TiO.sub.2 were weighed;

[0037] (2) The aforementioned reactants were placed in a ball-milling tank with the grinding medium of yttrium-stabilized zirconia balls and the dispersant of ethanol or acetone; ball-milling was carried out for more than 12 h until the reactants were thoroughly mixed; the mixture was dried to obtain a homogeneous mixture powder;

[0038] (3) The mixture powder was granulated in a mortar, and the detailed condition was: the pure water was added as the additive, and the weight ratio of pure water to the powder was 5%; mixed thoroughly; transferred the granulated powder into a 32 mm die, pressed at 416 MPa to obtain a green pellet; the green pellet was pulverized and ground in a mortar to obtain preliminary powder;

[0039] (4) The preliminary powder was transferred into a 1.2 mm die, pressed at a pressure of 2 MPa, followed by sintering in the air; sintering parameters included heating rate: 15.degree. C./min, temperature: 1420.degree. C., holding time: 3 h; after sintering, the product was naturally cooled down to room temperature to obtain a dense ceramic pellet;

[0040] (5) The surface of the dense ceramic pellet obtained in step (4), was polished by a 240-grit sandpaper and a 1200-grit sandpaper; annealed in the air; annealing parameters include heating rate: 15.degree. C./min, temperature: 1200.degree. C., holding time: 1 h; after annealing, the product obtained was naturally cooled down to room temperature to obtain the multiphase ceramic material.

Embodiment 2

[0041] Embodiment 2 is one of the embodiments in the present invention. The multiphase ceramic material of this embodiment has a general formula of A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2, wherein A is Nb, B is In, x=0.075, and n=2.

[0042] The detailed method to synthesize this embodiment comprised the following steps:

[0043] (1) 1.4952 g Nb.sub.2O.sub.5, 3.1233 g In.sub.2O.sub.3, and 9.2849 g TiO.sub.2 were weighed;

[0044] (2) The aforementioned reactants were placed in a ball-milling tank with the grinding medium of yttrium-stabilized zirconia balls and the dispersant of ethanol or acetone; ball-milling was carried out for more than 12 h until the reactants were thoroughly mixed; the mixture was dried to obtain a homogeneous mixture powder;

[0045] (3) The mixture powder was granulated in a mortar, and the detailed condition was: the pure water was added as the additive, and the weight ratio of pure water to the powder was 10%; mixed thoroughly; transferred the granulated powder into a 32 mm die, pressed at 416 MPa to obtain a green pellet; the green pellet was pulverized and ground in a mortar to obtain preliminary powder;

[0046] (4) The preliminary powder was transferred into a 1.2 mm die, pressed at a pressure of 2 MPa, followed by sintering in the air; sintering parameters included heating rate: 3.8.degree. C./min, temperature: 1200.degree. C., holding time: 3 h; after sintering, the product was naturally cooled down to room temperature to obtain a dense ceramic pellet;

[0047] (5) The surface of the dense ceramic pellet obtained in step (4) was polished with a 240-grit sandpaper and a 1200-grit sandpaper; annealed in the air; annealing parameters include heating rate: 5.degree. C./min, temperature: 1000.degree. C., holding time: 24 h; after annealing, the product obtained was naturally cooled down to room temperature to obtain the multiphase ceramic material.

Embodiment 3

[0048] Embodiment 3 is one of the embodiments in the present invention. The multiphase ceramic material of this embodiment has a general formula of A.sub.xB.sub.nxT.sub.1-(n+1)xO.sub.2, wherein A is Nb, B is In, x=0.0125, and n=3.

[0049] The detailed method to synthesize this embodiment comprised the following steps:

[0050] (1) 0.2492 g Nb.sub.2O.sub.5, 0.7809 g In.sub.2O.sub.3, and 11.3809 g TiO.sub.2 were weighed;

[0051] (2) The aforementioned reactants were placed in a ball-milling tank with the grinding medium of yttrium-stabilized zirconia balls and the dispersant of ethanol or acetone; ball-milling was carried out for more than 12 h until the reactants were thoroughly mixed; the mixture was dried to obtain a homogeneous mixture powder;

[0052] (3) The mixture powder was granulated in a mortar, and the detailed condition was: the pure water was added as the additive, and the weight ratio of pure water to the powder was 5%; mixed thoroughly; transferred the granulated powder into a 32 mm die, pressed at 416 MPa to obtain a green pellet; the green pellet was pulverized and ground in a mortar to obtain preliminary powder;

[0053] (4) The preliminary powder was transferred into a 1.2 mm die, pressed at a pressure of 2 MPa, followed by sintering in the air; sintering parameters included heating rate: 3.8.degree. C./min, temperature: 1420.degree. C., holding time: 3 h; after sintering, the product was naturally cooled down to room temperature to obtain a dense ceramic pellet;

[0054] (5) The surface of the dense ceramic pellet obtained in step (4) was polished with a 240-grit sandpaper and a 1200-grit sandpaper; annealed in the air; annealing parameters include heating rate: 5.degree. C./min, temperature: 1200.degree. C., holding time: 1 h; after annealing, the product obtained was naturally cooled down to room temperature to obtain the multiphase ceramic material with a giant dielectric constant.

Embodiment 4

[0055] Embodiment 4 is one of the embodiments in the present invention. The multiphase ceramic material of this embodiment has a general formula of A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2, wherein A is Nb, B is In, x=0.0125, and n=4.

[0056] The detailed method to synthesize this embodiment comprised the following steps:

[0057] (1) 0.2492 g Nb.sub.2O.sub.5, 1.0412 g In.sub.2O.sub.3, and 11.2312 g TiO.sub.2 were weighed;

[0058] (2) The aforementioned reactants were placed in a ball-milling tank with the grinding medium of yttrium-stabilized zirconia balls and the dispersant of ethanol or acetone; ball-milling was carried out for more than 12 h until the reactants were thoroughly mixed; the mixture was dried to obtain a homogeneous mixture powder;

[0059] (3) The mixture powder obtained was granulated in a mortar, and the detailed condition was: the pure water was added as the additive, and the weight ratio of pure water to the powder was 5%; mixed thoroughly; transferred the mixture powder into a 32 mm die, pressed at 416 MPa to obtain a green pellet; the green pellet was pulverized and ground in a mortar to obtain preliminary powder;

[0060] (4) The preliminary powder was transferred into a 1.2 mm die; pressed at a pressure of 2 MPa, followed by sintering in the air; sintering parameters included heating rate: 3.8.degree. C./min, temperature: 1420.degree. C., holding time: 3 h; after sintering, the product obtained was naturally cooled down to room temperature to obtain a dense ceramic pellet;

[0061] (5) The surface of the dense ceramic pellet obtained in step (4) was polished with a 240-grit sandpaper and a 1200-grit sandpaper, followed by annealing in the air; annealing parameters include heating rate: 5.degree. C./min, temperature: 1200.degree. C., holding time: 1 h; after annealing, the product obtained was naturally cooled down to room temperature to obtain the multiphase ceramic material with a giant dielectric constant.

[0062] FIG. 1 shows the XRD spectra of the multiphase ceramic material with a giant dielectric constant of embodiment 1 (1.25 at. % Nb.sup.5++2.5 at. % In.sup.3+) and embodiment 2 (7.5 at. % Nb.sup.5++15 at. % In.sup.3+). FIG. 1 illustrates that the materials prepared in embodiment 1 and embodiment 2 have two structures, that is, rutile titanium dioxide and orthogonal In.sub.2TiO.sub.5.

[0063] FIG. 2 shows the backscattered electron (BSE) images and the secondary electron (SE) images of the multiphase ceramic material with a giant dielectric constant of embodiment 1 (1.25 at. % Nb.sup.5++2.5 at. % In.sup.3+) and embodiment 2 (7.5 at. % Nb.sup.5++15 at. % In.sup.3+). FIG. 2 further demonstrates that the materials prepared in embodiment 1 and embodiment 2 have two phases, and the secondary phase is evenly dispersed in the primary phase.

[0064] FIG. 3 shows frequency-dependent dielectric properties of embodiment 1 (1.25 at. % Nb.sup.5++2.5 at. % In.sup.3+) at room temperature. FIG. 3 demonstrates that at the frequency range of 20 Hz to 2.times.10.sup.6 Hz, the dielectric constant of the ceramic material prepared in embodiment 1 (1.25 at. % Nb.sup.5++2.5 at. % In.sup.3+) is higher than 10,000 and it depends very little on frequency. When the frequency is lower than 2.times.10.sup.5 Hz, the dielectric loss is less than 0.05.

[0065] FIG. 4 shows temperature-dependent dielectric properties of embodiment 1 (1.25 at. % Nb.sup.5++2.5 at. % In.sup.3+) and 4 frequencies (100 Hz, 1 kHz, 10 kHz and 100 kHz) were selected. FIG. 4 shows that the dielectric constant of embodiment 1 (1.25 at. % Nb.sup.5++2.5 at. % In.sup.3+) is higher than 10,000 from -160.degree. C. to 170.degree. C. and it is almost temperature-independent. The dielectric loss is less than 0.05 from -50.degree. C. to 150.degree. C.

[0066] FIG. 5 is the backscattered electron (BSE) image of embodiment 2 (7.5 at. % Nb.sup.5++15 at. % In.sup.3+). Table 1 is the atomic ratio of elements of spots labelled out in FIG. 5, which was measured by the energy-dispersive spectroscopy (EDS).

TABLE-US-00001 TABLE 1 The atomic ratio of elements of spots labelled out in FIG. 5 EDS # Ti at. % Nb at. % In at. % 1 83.30 8.25 8.46 2 82.92 8.38 8.69 3 32.93 0.98 66.09

[0067] FIG. 1, FIG. 5, and table 1 show that the primary phase of the multiphase ceramic materials with a giant dielectric constant is Nb.sup.5+ and In.sup.3 + co-doped rutile TiO.sub.2, while the secondary phase is B.sub.2TiO.sub.5.

[0068] Table 2 summarizes the resistivity, the dielectric constant and the dielectric loss of the ceramic materials prepared in embodiments 1, 3, and 4 and a reference material:

TABLE-US-00002 TABLE 2 Resistivity, dielectric constant and dielectric loss of the materials of embodiments 1, 3, and 4 and a reference material Resistivity Dielectric constant Dielectric loss n General formula (.OMEGA. cm) (frequency f = 1 kHz) (frequency f = 1 kHz) 1 Nb.sub.1.25%In.sub.1.25%Ti.sub.97.5%O.sub.2 9.88 .times. 10.sup.10 57000 0.0031 (Reference material) 2 Nb.sub.1.25%In.sub.2.5%Ti.sub.96.25%O.sub.2 3.26 .times. 10.sup.11 12000 0.0048 3 Nb.sub.1.25%In.sub.3.75%Ti.sub.95%O.sub.2 2.53 .times. 10.sup.11 11000 0.0058 4 Nb.sub.1.25%In.sub.5%Ti.sub.93.75%O.sub.2 5.26 .times. 10.sup.11 10000 0.016

[0069] Compared with the reference material (1.25 at % Nb.sup.5+1.25 at % In.sup.3+), the materials of embodiments 1, 3 and 4 have higher resistivity, as well as a high dielectric constant (>10,000) and low dielectric loss (<0.05). This suggests that because the secondary phase is discontinuously and uniformly distributed at the grain boundary of the primary phase, it effectively blocks the movement of weakly bounded charges, contributing to high working voltage and breakdown voltage of the material. Meanwhile, the existence of the secondary phase does not cause the deterioration of the giant dielectric property of the material.

[0070] At last, it should be noted that the aforementioned embodiments are only used to illustrate the technical solutions of the present invention that does not limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solution of the present invention can be modified without deviating from the essence and scope of the technical solution of the present invention.

Claims

1. A multiphase ceramic material with a giant dielectric constant, wherein the multiphase ceramic material has a general formula of A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2; wherein A is at least one selected from the group consisting of Nb, Ta, V, Mo, and Sb, B is at least one selected from the group consisting of In, Ga, Al, Co, Cr, Sc, Fe (III), and a trivalent rare-earth cation; n is a molar ratio of B to A, 1<n.ltoreq.5, 0<x.ltoreq.0.1.

2. The multiphase ceramic material of claim 1, wherein a primary phase of the ceramic material is A5+ and B3+ co-doped rutile TiO2, a secondary phase of the ceramic material is B2TiO5; the secondary phase is evenly dispersed in the primary phase.

3. The multiphase ceramic material of claim 2, wherein the secondary phase is B.sub.2TiOs with an orthogonal structure.

4. The multiphase ceramic material of claim 1, wherein the multiphase ceramic material has a resistivity of higher than 10.sup.11 .OMEGA.cm.

5. The multiphase ceramic material of claim 1, wherein the multiphase ceramic material has a dielectric constant of higher than 10,000 at a frequency of 20 Hz to 2.times.10.sup.6 Hz; the multiphase ceramic material has a dielectric loss of less than 0.05 before 2.times.10.sup.5 Hz.

6. The multiphase ceramic material of claim 1, wherein the multiphase ceramic material has a dielectric constant of higher than 10,000 from -160.degree. C. to 170.degree. C.; the multiphase ceramic material has a dielectric loss of less than 0.05 from -50.degree. C. to 150.degree. C.

7. A method of preparing the multiphase ceramic material with a giant dielectric constant of claim 1, wherein the method comprises steps of: (1) weighing reactants, which comprise a titanium source, an A source, and a B source, according to a general formula of the multiphase ceramic material, A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2; (2) ball-milling in a ball-milling tank and drying to obtain a homogeneous mixture powder; (3) transferring the mixture powder into a mortar; pure water is added, and the weight of the pure water is 5%-10% of the weight of the mixture powder; mixing thoroughly; transferring the mixture powder into a die, pressing at a pressure of at least 400 MPa to obtain a green pellet; placing the green pellet in a mortar; pulverizing and grinding the green pellet to obtain a preliminary powder; (4) transferring the preliminary powder into a die; pressing at a pressure of at least 2 MPa, followed by sintering; sintering parameters comprise heating rate: 1.5.degree. C./min-15.degree. C./min, temperature: 1200.degree. C.-1500.degree. C., holding time: 1 h-24 h; after sintering, the product obtained is naturally cooled down to room temperature to obtain a dense ceramic pellet; (5) polishing a surface of the dense ceramic sheet, followed by annealing; annealing parameters comprise heating rate: 1.5.degree. C./min-15.degree. C./min, temperature: 1000.degree. C.-1200.degree. C., holding time: 1 h-24 h; after annealing, the product obtained is naturally cooled down to room temperature to obtain the multiphase ceramic material with a giant dielectric constant.

8. The method of claim 7, wherein in step 1, the titanium source is TiO.sub.2, the A source is A.sub.2O.sub.5, the B source is at least one selected from the group consisting of B.sub.2O.sub.3, B.sub.2(C.sub.2O.sub.4).sub.3, B.sub.2(C.sub.2O.sub.4).sub.3 hydrate, B(NO.sub.3).sub.3, B(NO.sub.3).sub.3 hydrate, B.sub.2(SO.sub.4).sub.3, B.sub.2(SO.sub.4).sub.3 hydrate, B.sub.2(CO.sub.3).sub.3, B.sub.2(CO.sub.3).sub.3 hydrate, B(C.sub.2H.sub.3O.sub.2).sub.3, B(C.sub.2H.sub.3O.sub.2).sub.3 hydrate.

9. The method of claim 7, wherein the ball-milling in step (2) comprises using ethanol or acetone as a dispersant, and using yttrium-stabilized zirconia balls as a ball-milling medium; ball-milling is performed for more than 12 hours; in steps (4) and (5), an atmosphere for the sintering and the annealing is air.

10. The method of claim 7, wherein the polishing of the surface in step (5) comprises rough polishing the surface by a 240-grit sandpaper, followed by finely polishing the surface by a 1200-grit sandpaper.

11. The multiphase ceramic material of claim 2, wherein the multiphase ceramic material has a dielectric constant of higher than 10,000 at a frequency of 20 Hz to 2.times.10.sup.6 Hz; the multiphase ceramic material has a dielectric loss of less than 0.05 before 2.times.10.sup.5 Hz.

12. The multiphase ceramic material of claim 3, wherein the multiphase ceramic material has a dielectric constant of higher than 10,000 at a frequency of 20 Hz to 2.times.10.sup.6 Hz; the multiphase ceramic material has a dielectric loss of less than 0.05 before 2.times.10.sup.5 Hz.

13. The multiphase ceramic material of claim 2, wherein the multiphase ceramic material has a dielectric constant of higher than 10,000 from -160.degree. C. to 170.degree. C.; the multiphase ceramic material has a dielectric loss of less than 0.05 from -50.degree. C. to 150.degree. C.

14. The multiphase ceramic material of claim 3, wherein the multiphase ceramic material has a dielectric constant of higher than 10,000 from -160.degree. C. to 170.degree. C.; the multiphase ceramic material has a dielectric loss of less than 0.05 from -50.degree. C. to 150.degree. C.

15. A method of preparing the multiphase ceramic material with a giant dielectric constant of claim 2, wherein the method comprises steps of: (1) weighing reactants, which comprise a titanium source, an A source, and a B source, according to a general formula of the multiphase ceramic material, A.sub.xB.sub.nxTi.sub.1-(n+1)xO.sub.2; (2) ball-milling in a ball-milling tank and drying to obtain a homogeneous mixture powder; (3) transferring the mixture powder into a mortar; pure water is added, and the weight of the pure water is 5%-10% of the weight of the mixture powder; mixing thoroughly; transferring the mixture powder into a die, pressing at a pressure of at least 400 MPa to obtain a green pellet; placing the green pellet in a mortar; pulverizing and grinding the green pellet to obtain a preliminary powder; (4) transferring the preliminary powder into a die; pressing at a pressure of at least 2 MPa, followed by sintering; sintering parameters comprise heating rate: 1.5.degree. C./min-15.degree. C./min, temperature: 1200.degree. C.-1500.degree. C., holding time: 1 h-24 h; after sintering, the product obtained is naturally cooled down to room temperature to obtain a dense ceramic pellet; (5) polishing a surface of the dense ceramic sheet, followed by annealing; annealing parameters comprise heating rate: 1.5.degree. C./min-15.degree. C./min, temperature: 1000.degree. C.-1200.degree. C., holding time: 1 h-24 h; after annealing, the product obtained is naturally cooled down to room temperature to obtain the multiphase ceramic material with a giant dielectric constant.

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